The present invention relates to a flexible thin layer electrochemical cell and more particularly, but not exclusively, to materials for the manufacture of such a cell and a method of manufacture thereof.
The present invention relates to the manufacture of electrochemical cells which are used as power sources by converting chemical energy to electrical energy, including batteries and other types of electrochemical components which share structural features therewith, including in particular capacitors and electrolytic capacitors. More particularly, the present invention relates to a primary or rechargeable electrochemical cell to be used as a primary or rechargeable battery which accomplishes the conversion of chemical energy to electrical energy using perhaps a wet (e.g., liquid state) electrolyte, yet maintains a flexible thin layer configuration.
The most common type of battery is the cylindrical battery. Cylindrical batteries include the bobbin type, in which one electrode is a central axis and the other electrode is outwardly located of the cylinder with electrolyte and a separator therebetween.
A second type of cylindrical battery is the jellyroll battery. In the jellyroll battery, an anode and a cathode are wound tightly around a mandrel with a separator therebetween.
The ever-growing development of miniaturized and portable electrically powered devices such as for example cellular phones, voice recording and playing devices, watches, motion and still cameras, liquid crystal displays, electronic calculators, IC cards, temperature sensors, hearing aids, pressure sensitive buzzers, etc., has generated a need for compact batteries for their operation. Currently popular for such applications are button cells which comprise flattened cylinders having an upper closure and a lower closure. One electrode is attached to the upper closure and the second electrode is attached to the lower closure of the button. The two halves of the cylinder are then sealed together to form the complete battery.
Nevertheless, the button battery has a relatively large thickness due to its need for upper and lower surrounding metal walls. The dimensions of the battery bound the extent of miniaturization for many devices.
There thus arises a need for reliable thin layer electrochemical cells to be used as batteries.
Batteries can be broadly classified into three categories in which batteries of the first category include wet electrolytes (i.e., liquid state batteries), and batteries of the second category include solid state electrolyte. There is also a third, gel type.
Solid state batteries have an inherent advantage, they do not dry out and do not leak, they suffer major disadvantages when compared with liquid state batteries since, due to limited diffusion rates of ions through a solid, their operation is temperature dependent to a much larger extent, and many operate well only under elevated temperatures. Furthermore, the limited diffusion rates result in batteries with low ratio of electrical energy generated vs. their potential chemical energy.
Liquid state thin layer batteries typically include a positive and negative active insoluble material layer put together with a separator interposed therebetween, which separator is soaked with a liquid electrolyte solution, thus functioning as an electrolytic liquid layer. Such batteries, examples of which are disclosed in U.S. Pat. No. 4,623,598 to Waki et al., and in Japanese Pat. No. JP 61-55866 to Fuminobu et al., are sealed within a sheathing film to prevent liquid evaporation, and therefore form closed electrochemical cells. Being closed cells, these batteries tend to swell upon storage due to evolution of gases which is a fatal problem in thin layer batteries having no mechanical support, the pressure imposed by the accumulated gases leads to layer separation, thus rendering the battery inoperative.
Means to overcome this problem include (i) the use of a polymer increased viscosity agent, such as hydroxyethylcellulose, applied to adhere (i.e., glue) the battery layers together, thus overcoming the problem of lack of solid support; and, (ii) the addition of mercury, which is particularly useful in the prevention of hydrogen formation.
It is noted, however, that the polymer is limited in its effectiveness and the mercury is an environmental hazard. Thus the problems are not successfully overcome.
A way to solve the swelling problem was disclosed in U.S. Pat. No. 3,901,732 to Kis et al. in which a gas-permeable electrolyte-impermeable polymeric material which allows venting of undesirable gases formed within the battery while preventing any electrolyte loss from the battery is used as a sheathing film to enclose the battery cell.
However, a more direct and efficient way to avoid undesired gas accumulation in liquid state thin layer batteries would be to provide these batteries as open cells for facilitated release of gases, while at the same time to provide means to avoid liquid evaporation and drying out of the battery.
U.S. Pat. 5,652,043 thus provides a flexible thin layer open liquid state electrochemical cell, which can be used as a primary or rechargeable power supply for various miniaturized and portable electrically powered devices of compact design. The cell includes a wet electrolyte, yet maintains a flexible, thin and open configuration, thus devoid of accumulation of gases upon storage. The cell comprising a first layer being an insoluble negative pole, a second layer being an insoluble positive pole and a third layer being aqueous electrolyte, the third layer being disposed between the first and second layers and including a deliquescent material for keeping the open cell wet at all times; an electroactive soluble material for obtaining required ionic conductivity; and, a water-soluble polymer for obtaining a required viscosity for adhering the layers. The electrochemical cell therein described is preferably produced using a suitable printing technology.
International Patent Application WO 98/56458 discloses a flexible thin layer open cell and discusses a method of manufacture thereof.
Flexible thin layer lithium cells were reported in Scientific American October 1997, as follows:
The lithium power source is a recent development in mobile power sources. The battery is flat and flexible, like a stick of chewing gum (one of its manufacturers refers to its product as a film battery because its batteries are also reminiscent of film frames). These batteries, which could soon be as thin as 0.2 millimeter, can be manufactured in long, continuous strips, which should reduce production costs. Both NiCd and NiMH cells can also be produced using the chewing gum format.
Generally, a battery of the above-described kind is manufactured by printing different layers one on top of the other. Manufacture begins with a first electrode, upon which a separator containing electrolyte is printed, and then a second electrode may be printed over that. The layers are packaged in plastic; the plastic layers being attached from around the edges by the insertion of a sealing compound.
According to a first aspect of the present invention there is thus provided a method of using a lamination process to make a flexible thin layer electrochemical cell having a plurality of layers including a first and a second electrode layer with a separator in between and wherein the separator serves as a lead element upon which the other layers are laminated,
According to a second aspect of the present invention there is provided a method of manufacturing a thin layer electrochemical cell comprising the steps of:
providing a separator layer;
providing a positive electrode layer,
providing a negative electrode layer, and
laminating together the positive and negative electrode layers onto the separator layer.
A preferred embodiment comprises the step of impregnating a nonconductive material to form a non-conductive region within at least one of the layers.
Preferably, the step of laminating further comprises impregnating a non-conductive material to form a non-conductive sealed region within at least one of the layers.
Preferably, the non-conduction region is formed as a border defining an outer boundary of the cell.
Preferably, the non-conduction region extends through at least two of the layers.
Preferably, the non-conduction region extends through all three of the layers.
Preferably, the thin layer electrochemical cell is an open thin layer electrochemical cell.
A preferred embodiment comprises the step of applying a partial layer of non-conduction material to the separator layer.
Preferably, the non-conductive material is an adhesive material.
Preferably, the adhesive material is any one of a group comprising urethane acrylate, epoxy acrylate, other cross-linked acrylates, and cured acrylates.
Preferably, the non-conduction material is selected from the group consisting of a hot melt material, a hot melt pressure sensitive material and a UV curable pressure sensitive material.
A preferred embodiment comprises comprising the step of adding an impregnation agent to the partial layer.
Preferably, the impregnation agent is selected from the group consisting of polyisobutylene, ethyl cellulose, a fluoro polymer, an acrylic resin, a vinyl resin, and polyurethane.
According to a third aspect of the present invention there is provided a separator layer for use in the production of a flexible thin layer electrochemical cell, the separator layer comprising an impregnator applied thereto, which impregnator is susceptible to impregnate the separator layer during lamination processing applied to the layer to form the cell.
Preferably, the impregnator comprises an adhesive material.
Preferably, the adhesive material is selected from the group consisting of a hot melt material, a hot melt pressure sensitive material and a UV curable pressure sensitive material.
Preferably, the impregnator comprises an impregnation agent operable to cause impregnation into at least one of the layers of at least one material of the impregnator.
Preferably, the impregnator is operable to restrict electrical conductivity in a region of any electrically conductive layer into which it is absorbed.
Preferably, the impregnation agent is selected from the group consisting of polyisobutylene, ethyl cellulose, a fluoro polymer, an acrylic resin, a vinyl resin, and polyurethane.
A preferred embodiment has a first side and a second side and the impregnator is applied on both of the first side and the second side for lamination thereto of further layers to form the cell.
A preferred embodiment has a positive electrode layer laminated to the first side and a negative electrode layer laminated to the second side, each electrode layer further comprising electrolyte.
According to a fourth aspect of the present invention there is provided a flexible thin layer open electrochemical cell comprising a plurality of layers laminated to one another.
In a preferred embodiment, layers comprise a conduction inhibitor absorbed within the layers to form non-conduction regions.
In a preferred embodiment, the conduction inhibitor comprises an adhesive material.
In a preferred embodiment, the adhesive material being is selected from the group consisting of a hot melt material, a hot melt pressure sensitive material and a UV curable pressure sensitive material.
In a preferred embodiment, the conduction inhibitor further comprises an impregnation agent.
In a preferred embodiment, the impregnation agent including is selected from the group consisting of polyisobutylene, ethyl cellulose, a fluoro polymer, an acrylic resin, a vinyl resin, and polyurethane.
Preferably, the non-conducting regions are arranged to define borders of the cell.
Preferably, the adhesive is suitable for laminating the layers together in a lamination process.
Preferably, the base layer comprises an impregnator located thereon, which impregnator is operable to impregnate the separator layer during lamination processing applied to the layer to form the cell.
Preferably, the impregnator comprises an adhesive suitable for adhering the layers during lamination processing.
Preferably, the adhesive is selected from the group consisting of a hot melt material, a hot melt pressure sensitive material and a UV curable pressure sensitive material.
Preferably, the impregnator further comprises an impregnation agent operable to cause impregnation into the layers of at least one material of the impregnator.
Preferably, the impregnation agent is selected from the group consisting of po, ethyl cellulose, a fluoro polymer, an acrylic resin, a vinyl resin, and polyurethane.
A preferred embodiment comprises a first side and a second side and the impregnator is superimposed on both of the first side and the second side for lamination thereto of further layers to form the cell.
A preferred embodiment comprises a positive electrode layer laminated to the first side and a negative electrode layer laminated to the second side, each electrode layer further comprising electrolyte.
Preferably, the impregnation region extends into the electrode layers.
Preferably, the impregnator is operable to form non-conducting impregnation regions in the electrode layers.
Preferably, the non-conducting regions define a border closing a region of the layer.